The assignee of the present invention has recently developed a dual axis mirror with a single reflection surface described in U.S. patent application Ser. No. 10/384,861 filed Mar. 10, 2003 entitled “Laser Printer Apparatus Using a Pivoting Scanning Mirror”. This dual axis mirror uses a first set of torsional hinges for providing oscillating beam sweep such as a resonant beam sweep and a second set of torsional hinges that selectively moves the oscillating beam sweep in a direction orthogonal to the oscillating or resonant beam sweep. By dynamically controlling the orthogonal position of the beam sweep to compensate for movement of the photosensitive medium, both directions of the resonant beam sweep may be used to print parallel image lines.
The devices of the present invention also uses torsional hinges. However, rather than a reflective surface or mirror, the device of the present invention supports a “functional surface” with the torsional hinges. Just as the mirror or reflective surface was caused to pivotally resonate about its torsional hinges, the functional surface of the present invention can be caused to pivotally resonate. The resonant frequency of the oscillation surface can then be measured to determine change in mass.
A dual axis resonant MEMS device may be fabricated out of a single piece of material (such as silicon, for example) using semiconductor manufacturing processes. The layout consists of a functional surface having dimensions on the order of a few millimeters supported on a gimbals frame by two silicon torsional hinges. The gimbals frame is supported by another set of torsional hinges, which extend from the gimbals frame to a support frame or alternately the hinges may extend from the gimbals frame to a pair of hinge anchors. A similar single axis mirror device, of course, eliminates the gimbals frame altogether by extending the single pair of torsional hinges of the device directly to the support frame or support anchors.
One presently used technique to pivotally resonate the device about a first axis is to provide electromagnetic coils on each side of the mirror and then drive the coils with an alternating signal at the desired sweep frequency. Electromagnetic coils may also be used to provide the orthogonal movement. However, when electromagnetic coils are used to provide orthogonal movement, rather than an alternating voltage, a specific DC voltage is connected across the coils to precisely position the orthogonal movement. The present invention discloses improved techniques for generating resonant pivoting.